1. Field of the Invention
This invention relates generally to the field of multimedia systems. More particularly, the invention relates to a multimedia system capable of concurrently demodulating and decoding a plurality of multimedia streams transmitted from a satellite or a cable network.
2. Description of the Related Art
Digital broadband video systems, such as digital cable or satellite, multiplex many television channels onto a single carrier. In the cable world, the carriers are modulated using Quadrature Amplitude Modulation (“QAM”). In the satellite world, the carriers (known as transponders) are modulated using Quadrature Phase Shift Key (“QPSK”) modulation. In residential satellite/cable systems, these carriers typically have a net bandwidth of 20–40 Mbits/s.
As illustrated in FIG. 1, a conventional digital receiver 100 is comprised of a tuner 110 for locking on to a signal from a single transponder at a specified frequency and downconverting the signal to baseband. The tuner 110 receives the transponder signal from a satellite dish 105 with one or more low noise block downconverters (“LNBs”). The signal coming from the transponder has either a clockwise or counterclockwise polarization (or horizontal vs. vertical for fixed satellite service (“FSS”) systems satellite systems). Each LNB, which can be thought of as an antenna, can selectively listen to either polarization. The LNB also moves the signal from the satellite transmission band (Ka or Ku) into the L-Band, 950–2100 MHz.
The signal is then digitally sampled via an analog-to-digital (“A/D”) converter 120 and demodulated via a QPSK demodulator 130 (or, in the case of digital cable, a QAM demodulator). Noise and other types of interference may be introduced in the signal during transmission (e.g., by the tuner and/or the LNB). When demodulating the signal, the QPSK demodulator 130 attempts to remove these unwanted portions of the signal using a combination of filters (e.g., band-pass FIR filters for removing noise, root-raised cosine filters for removing inter-symbol interference, . . . etc).
The demodulated signal is then transmitted to a Viterbi decoder 140 (or other type of forward-error-correction decoder) which attempts to correct bit errors caused by signal noise. In particular, the Viterbi algorithm determines the most likely transmitted bit sequence using statistical correlation of the bit sequence actually received by the system. Accordingly, the original bit sequence may be reconstructed, even in the presence of a significant amount of noise.
After additional processing, the Viterbi-decoded signal is input to a Reed-Solomon decoder 150 (or similar block-based decoder). Reed-Solomon codes are block-based error correcting codes. Before transmission, a Reed-Solomon encoder (not shown) adds extra “redundant” bits to each block of data. The Reed-Solomon decoder 150 processes each block and attempts to correct any errors and recover the original data. The number and type of errors that can be corrected depends on the characteristics of the particular Reed-Solomon code employed.
Following Reed-Solomon decoding, a single MPEG-2 transport stream containing video data for a single channel (e.g., HBO) is demultiplexed and further processed by the system. If the system is equipped with a mass storage device (e.g., such as a Tivo™ or Replay TV™ system), the MPEG-2 stream may be stored for later viewing. In addition, “trick modes” such as pause and rewind for live television broadcasts may be implemented on the system. Alternatively, or in addition, the signal may be decoded by an MPEG-2 decoder (not shown) and rendered on a television display.
One limitation of the system illustrated in FIG. 1 is that it is only capable of processing data from a single transponder at any given time. In order to concurrently process data from a group of n transponders, all of the logic illustrated in FIG. 1 must be multiplied by n, resulting in significant additional manufacturing costs. Given that satellite systems typically transmit multimedia data over between 24 to 32 transponders, a system for concurrently processing data transmitted over all available transponders would be prohibitively expensive to manufacture using current satellite receiver technologies.
A receiver system capable of concurrently processing data from multiple transponders would provide many benefits to end users, especially if the system included a high performance mass storage device (a 40+ Gbyte hard drive with an ATA-100 interface). For example, channels from several different transponders could then be concurrently stored on the on the mass storage device, either for long term storage or for “trick modes.” Such a system would allow users to watch any program being broadcast from the beginning by continually buffering each program (or subset thereof) for a predetermined period of time (e.g., until the program broadcast has ended).
Accordingly, what is needed is a system and method for concurrently processing content from multiple transponders and/or QAMs which is not prohibitively expensive to manufacture.